The digital indication on the speedometer seems quite accurate but I have only compared occasionally with speed cameras.

Power and torque is measured on the crank shaft. I have heard you will have a loss through the primary and secondary transmission of between 10% to 15% (i.e. on the wheels). Someone else might have more exact information, though.

the loss of 10 to 15% of power from the crankshaft to the wheels its in bikes, I think in cars its between 20 to 30%

thanks

That is a bit oversimplified, isn't *necessarily* true, and entails myriad issues

Most SAE rated HP is at the flywheel; as well, drivetrain losses will depend on many things and can vary depending on both sprung/ unsprung weight (weight of the monocoque and engine/ wheels and suspension), and transmission type.

For example, the new DSG transmissions emerging on supercars today, such as implemented in the F149 California, F458 Italia, Nissan GT-R ... incur less power loss penalty due to the efficiency of the transmission to transmit the available horsepower.

The super quick shifting mechanism allows the DSG transmission to keep the rpms higher in the rev band between shifts, allowing peak horsepower in any given gear to remain continuous. In this case, a % of the drivetrain losses are offset by the car remaining in peak horsepower longer

It is a bit more sophisticated and also a.o. depends on how measured, FWD v RWD v AWD, etc.

However, in crude practice, 20-25% losses are commonly observed/assumed in dyno-tests indeed:

"Because of frictional and mechanical losses in the various drivetrain components, the measured rear wheel brake horsepower is generally 15-20 percent less than the brake horsepower measured at the crankshaft or flywheel on an engine dynamometer.[4] Other sources, after researching several different "engine" dyno software packages, found that the engine dyno user can integrally add "frictional loss" channel factors of +10% to +15% to the flywheel power, raising the claim that 20% to 25% or even more power is actually lost between the crankshaft at high power outputs."

No they don't, not anymore although they certainly used to in the old days. The 599 was dyno'd by EVO Magazine and shown to be delivering more hp than Ferrari claims (I think it was around 15bhp more than Ferrari's figures). There was another Ferrari they did the same to, same result, but can't remember which one it was. Harry Metcalfe also had his 550 dyno'd and it delivered very close to claimed figures even though the car was 6 years old at the time.

Claimed speed is also more accurate these days. The 550 was given 199mph but it does not achieve it. A German magazine tested the car at 308 km/h, which is just over 191mph. Subsequent cars have been closer to their claimed speed. After all, the topspeed has hardly risen even with massive power increases and aerodynamic improvements.

No they don't, not anymore although they certainly used to in the old days. The 599 was dyno'd by EVO Magazine and shown to be delivering more hp than Ferrari claims (I think it was around 15bhp more than Ferrari's figures). There was another Ferrari they did the same to, same result, but can't remember which one it was. Harry Metcalfe also had his 550 dyno'd and it delivered very close to claimed figures even though the car was 6 years old at the time.

Claimed speed is also more accurate these days. The 550 was given 199mph but it does not achieve it. A German magazine tested the car at 308 km/h, which is just over 191mph. Subsequent cars have been closer to their claimed speed. After all, the topspeed has hardly risen even with massive power increases and aerodynamic improvements.

Onno

I'll say I do not know of the current items, and your explaination does make sense: So, I'll reword to say 'in the past'

No they don't, not anymore although they certainly used to in the old days. The 599 was dyno'd by EVO Magazine and shown to be delivering more hp than Ferrari claims (I think it was around 15bhp more than Ferrari's figures). There was another Ferrari they did the same to, same result, but can't remember which one it was. Harry Metcalfe also had his 550 dyno'd and it delivered very close to claimed figures even though the car was 6 years old at the time.

I remember that article.

First time they did the test, the 599 bhp was a lot lower. Then they changed the tyres and the bhp shot up.

As for % transmission loss, it's anywhere between 15 and 25% depending on who you talk to.